1. Field of the Invention
The present invention relates to an audio signal processor, which can be connected to a network through which an audio signal is transmitted, and an audio signal processing system including such an audio signal processor.
2. Background Art
In the related art, various network systems for transmitting the data between a plurality of devices are known.
For example, an audio network system for transmitting an audio signal between a plurality of nodes is known, and this is used in concerts, plays, music production, private broadcasting, and so on. Known examples of such an audio network system include CobraNet (trademark) and EtherSound (trademark) disclosed in “CobraNet™, [online], Balcom Co., Ltd. [Retrieved on Mar. 21, 2006], Internet <URL: http://www.balcom.co.jp/cobranet.htm>” and “Carl Conrad, EtherSound™ in a studio environment, [online], Digigram S. A., [Retrieved on Mar. 21, 2006], Internet <URL: http://www.ethersound.com/news/getnews.php?enews_key=101>”.
In addition, a network system disclosed in JP-A-2009-94589 is proposed.
In the network system disclosed in JP-A-2009-94589, not only an audio signal but also a control signal, such as an Ethernet (registered trademark) frame, can be stably transmitted from an arbitrary device included in the system to another arbitrary device by making a frame circulate periodically through a ring-shaped transmission path, which is formed by each device included in the system, and making each device read and write the required information from and into the frame.
Moreover, JP-A-2008-72363 discloses a technique in which in a network system where a frame is made to circulate periodically as described above, a master node generates a word clock (sampling clock) and transmits a frame at a timing based on the clock while other nodes generate a word clock by delaying a periodical frame receiving timing as a reference by an appropriate time. In this way, a word clock with the same period and phase as in the master node can be generated in each node. That is, a word clock can also be simultaneously transmitted by transmission of a frame.
In the network systems disclosed in JP-A-2009-94589 and JP-A-2008-72363, however, it is necessary to make a frame circulate a transmission path once within a predetermined period while reading and writing the data from and into a frame for signal transmission by a device.
Therefore, there is a problem that the number of devices which could be built into a system, and the physical length (mainly depending on the length of a cable for connection between devices) of a transmission path are restricted.
In order to cope with such a problem, it may be considered to adopt a configuration in which a bridge device connectable to a plurality of transmission paths is provided in a network system and the plurality of transmission paths are connected to each other through the bridge device.
In the case of adopting the configuration in which the plurality of transmission paths are connected to each other, if the entire system is made to operate on the basis of the same word clock, the word clock needs to be appropriately transmitted from the transmission path, to which a device serving as a word clock source of the entire system belongs, to another transmission path.
Moreover, if the word clock source is changed to another device, a period of time for which signal transmission is not possible occurs until transmission of a frame based on a word clock from a new word clock source is started after the word clock source before the change stops supply of a word clock. Moreover, when a word clock source is changed to a device belonging to a different transmission path from that until then, it takes time to shift the system to the state in which a word clock is transmitted from the new word clock source to the entire system. As a result, the period of time for which signal transmission is not possible is increased.